1. Field of the Invention
The present invention relates to an optical device.
2. Description of the Related Art
In general, on a side of a display surface of a display device, such as a liquid crystal display (Liquid Crystal Display: LCD), a cover that is formed of a transparent substrate is disposed so as to protect the display device.
However, when such a transparent substrate is disposed on the display device, and when a displayed image of the display device is attempted to be viewed through the transparent substrate, often, an object that is disposed in the vicinity can be reflected. When such a reflection occurs on the transparent substrate, it may become difficult for a person viewing the displayed image to view the displayed image, and the person viewing the image may have an unpleasant impression. Especially, for cover glass that is installed inside a vehicle, a strong light source that is represented by sunlight can be reflected. Thus, it can become very difficult to view a displayed image, and it is possible that driving is adversely affected because necessary information cannot be read.
Thus, for preventing such a reflection from occurring, for example, a method has been adopted that is for implementing an anti-glare process that is for forming an uneven shape on the surface of the transparent substrate.
Note that Patent Document 1 discloses a method of evaluating a reflection on the display device by using a special device.    Patent Document 1: Japanese Unexamined Patent Publication No. 2007-147343
As described above, Patent Document 1 shows the method of evaluating the reflection on the display device using the special device.
However, optical characteristics that are required for cover glass that is installed inside a vehicle is not limited to reduction of reflection. Namely, cover glass that is installed inside a vehicle may be required to have predetermined levels of optical characteristics, such as for a resolution, reflection image diffusiveness, and sparkle, respectively. Accordingly, for selecting a transparent substrate, it may be insufficient to consider only one of the optical characteristics. Often, there may arises a need to consider a plurality of optical characteristics at the same time.
The resolution that is described here is for representing whether and to what extent an image that matches a displayed image can be obtained when the displayed image is viewed through a transparent substrate. Further, the reflection image diffusiveness is for representing to what extent a reflected image of an object that (e.g., a light) is disposed in the vicinity of the transparent substrate matches the original object. Furthermore, the sparkle is for representing to what extent unevenness of a bright spot is observed that occurs when light (an image) from the display image passes through the transparent substrate, the light is reflected by the surface of the transparent substrate, and the scattered light beams mutually interfere.
Among the optical characteristics that are required for the transparent substrate, there are often characteristics that are in tradeoff relationships. For example, in general, in order to enhance the reflection image diffusiveness, the anti-glare process is applied to the surface of the transparent substrate. However, when such an anti-glare process is applied, a resolution of the transparent substrate tends to be lowered. In this manner, when the anti-glare process is to be applied to the transparent substrate based on a plurality of optical characteristics, it may become difficult to select a proper anti-glare process.